Telephone substation circuits



1,624,057 F. w. M KowN ET m.

TELEPHONE SUBSTRTI 0N CIRCUITS April 12, 1927.

Filed June 1, 1925 INVENTORS Z 719105514 Djetga ATTORNEY Patented Apr.12, 1927.

UNITED STATES A'TEINT Q F F IC E FREDERICK w. MoKGWN, on EneLEwoon, ANDEGILNHARD DIETZE, or wEsT'EIELn, NEW JERSEY, ASSIGNORS TO AMERICANTELEPHONE Ann TELEGRAPH COMPANY,

13. CORIEORATION OF NEVT'YORK.

TELEPHONE STJBSTA'J'.ION CIRCUITS.

Application filed June 1, 1925. "Seria1:N0."34,164.

This invention relates to circuit arrangements for signaling systemswherein signals may be either transmitted from or received at the samestation. In its more specific as- 5 pect this invention is embodied in asubscribers telephone station hereinafter termed, in accordance withcommon usage, a substation, and more particularly in the combination ofa substation and a telephone set.

The object of this invention is to provide an economical signalingcircuit arrangement which in co-operative combination with a similar andequal signaling circuitarrangement at the distant end-of a telephoneline, shall deliver a large proportion of energy to the receivingapparatus of said signaling circuit arrangement atthe distantend o'f-theline.

A further object is to provide a substation consisting of a transmitterand a receiver of the electromagnetic type, having a plurality ofwindings and arranged for invariable two-way communication over a linehaving given impedance and length. In other 25 words, the object of theinvention is to provid signaling means characterized by a minimum numberof elements.

The simplest form of substation for invariable two-way communication isthat in which the receiver and transmitter are connected in series witheach other across a telephone line, the transmitter and receiver eachhaving a resistance which is equal to onehali of the line impedance. Insuch an arrangement the over-all efficiency is a maXimum for aninvariable set, even though 50 per cent of the energy delivered by theline to the substation is wasted in the transmitter and only 50 per centof the energy available at the transmitter reaches the line. Further,such an arrangement labors under the disadvantage of full side tone.

In the types of substation circuits now in use, the transmitter has aresistance which is about one-twelfth of the line impedance. Such atransmitter cannot be employed in the simple series circuit if theconditions for maximum energy transfer are to be satisfied. To improvethe efficiency of the subcommunication is established.

station it has :beencustomary to employ a transformer or induction coilin the substation circuit in order tostep up the transmitter resistance.Inthiearrangements of the present invention, however, the inductioncoil'ihasrbeen eliminated and its function. has been :relegated :to the'receiver.

The invention will be more fully understood by ieference to theaccompanying drawing, in which vFigure 1 is a substation havinga minimumnumber of elements, Fig. 2 shows a substation in Which an equalizingresistance is .connected across the line for the purpose of reducingside tone on short loops. Fig. 3 isa modification-of Fig. 1, and Fig. 4,shows a substation in which the windings of the receiverare proportionedso as to reduce side tone.

In order to illustrate the scope of the in vention' and elucidate \theprinciples on which the embodiments rest, a general theoreticaldiscussion will :now %be given which applies stothe substations shown inthe drawing of this specification. In this discussion and the equationsand formulae included in thespeci-fieatiouythesubscripts I, IE andRtavill refer to transmitter,"line and receiver respectively. 1llllS,.I'1', I and I will denote the currents'fiowing in thetransmitter. line and receiver, respectively, whileZ will denote theimpedance-of the transmitter, Z the impedance of theline, etc.

Consider the substation illustrated in 1 consisting of a "two-elementtransmitter and receiver connected to a line of given impedance. Inpractice, the line connects two similar andequal substations betweenwhich For transmitting, consider the transmitter as having a voltage Ein series with each transmitter button. the two transmitter buttonshaving equal impedances. By .Kirchoflis laws,

In-the foregoing expressions A and B iii} Leeann? refer to the twowindings of the electromagnetic receiver used in the substation, Z, andZ; refer to the sel'f-impedances of said windings, and Z refers to themutual impedance of said windings, Solving these equationssimultaneously, (bearing in mind that the impedance of a receiver havingtwo windings, A and B, which are series aiding, is

ZA+ZB+2Zo the current in the line, L, is

W E (Z ZZ (E Z Z (Z +2Z (Z Z 1) and the current in winding B, T is"E(2ZA+2ZL+ZM+ZT) ZL (Z13 ZT)2 Tn deriving the values of the currents inthe respective branches when signals are being received at thesubstation, consider a voltage 0 to be in series with the line L, thenThe expression for the value of the current in the line L, 1 whensignals are being received at the substation is The current T in thelower branch, which includes the winding B of the receiver of thesubstation is The transmitting eificiency or the substation may beexpressed as the square root of the ratio of the power actually sentinto the line by the transmitter of the substation to the maximum powerthat could be sent into the line by the transmitter of the idealinvariable substation. The transmitting elficiency may be determinedfrom the expression PA Pi in which P is the power actually delivered tothe line, or

mil ew/E and P the power in the ideal invariable substation circuit, isdetermined from the expression 1 E i/Pi c mi Substituting the value ofthe current in the line, L, derived h-ereinbefore, and bearing in mindthat ZM W/ AZ; approximately, the transmitting etliciency becomes 1/m'(B w/ ;l ZA+ZL+ZT) ZB+2ZT) (ZM ZT 2 J T m I,

and

Defining the effective current in the receiver as the quotient of theampere turns and the turns of the receiver, the r ceiving efficiency maythen be determined from the ex ion The power in the receiver of aninvariable substation circuit when a voltage is acting in series withthe transmitter at the same substation is known asside tone. The sidetone efiiciency is PA P in which R, is the power actually delivered tothe receiver at the same substation, and P is the value obtained fromthe expression the impedance of the transmitter, Z being merely aresistance at normal telephonic frequencies. The value of the current inthe receiver, I having been determined hereinbefore, the side toneefliciency will then be found to be The transmitter may be considered agenerator having a fixed internal resistance which sends current throughthe receiver at the same substation and through the line in seriestherewith. VV'hile transmitting, the energy in the receiver is wasted sofar as transmission to the substation at the distant end of the line isconcerned. Also, while receiving, the power delivered to the transmitteris wasted. In order to have the maximum energy transfer between the lineand the substation the generator element should be equal to the elementto which power is being delivered. Therefore, in order to obtain themaximum energy transfer between the line and the substation whiletransmitting, the line should have the same impedance as thetransmitter, and while receiving, the receiver should have the sameimpedance as the line. i rom the equations given her-einbei'ore themaximum energy transfer between the line and the substation may beobtained when the impedance of the substation, Z has the magnitude Theenergy ratio Y is known in the art as transmitting eficienoy 2 receivingefiiciency Substituting the values for the transmitand receivingefliciencies, respectively, the energy ratio Y will be found to equal ZBZZ cos 6 in which 6 is the receiver angle, the tangent of 6 being theratio of the reactance component to the resistance component of a singlewinding of the electromagnetic receiver, 6 being of substantially equalmagnitude tar both oi? the windings.

T he embodiments of this invention disclose arrangements in which thetransmitter, receiver and line are effectively in parallel. Side tonemay become objectionable on short loops because noises at thesubstation, which EXli-G the transmitter, will produce sounds in thereceiver. Furthermore, the operator talks in his own ear, and if hetalks very loudly the effect of side tone may make it very uncomtortablefor him. It is therefore important that on short loops the side tone bekept very low.

On inspection of the formula for the side ton-e efficiency it will benoted that the side tone etiiciency varies in accordance with thempedance of the line, the side tone increasthe impedance of the lineincreases.

In arrangements of the parallel type, the side tone may be reduced bymaking the impedance of the substation .set higher than the impedance ofthe line.

Fig. 2 shows an arrangement of the par-- allel type in which anequalizing resistance H is connected in shunt with the circuit. Thus thecurrent in the line is lowered, the side tone being reduced to an evengreater extent than the efiiciency. A condenser C is serially connectedto the ringer U for ringing purposes. Figs. 3 and 4 are similar to Fig.l, the ringing circuit, consisting of the ringer U and condenser C,being shown con nected across line L. In Fig. 3 the transmitter isconnected to terminal V the windings of the receiver are proportionedfor maximum efficiency. In Fig. 4 the transmitter is connected toterminal VJ. Point lV may be chosen to proportion the windings of thereceiver so as to considerably reduce side tone, thus involving someloss in efficiency also. It will therefore be desirable to con nect thetransmitter to terminal V on long loops and to terminal N on shortloops.

The accompanying formulae give satisfactory results and the methods bywhich they are derived enable one skilled in the art to compute thesubstation constants when desired.

It will be understood that while certain embodiments have beenspecifically illustrated and described as embodied in a telephonesubstation, it is capable of many and varied embodiments which render itapplicable to other kinds oi signaling systems. Consequently, theinvention is not to be limited to the particular form and use hereindisclosed but is to be limited only by the appended claims. It will befurther understood that in this specification the word substation isemployed in its generic sense, and that consequently, its significanceis not limited to a subscribers telephone station but embraces broadly atelephone staton including a repeater station for relaying telephonicsignals.

What is claimed is:

1. A circuit comprising two branches, devices tor converting sound wavesinto electric waves, means for simultaneously actuating said devices,and means for converting electric waves into sound waves, said lattermeans consisting of two closely coupled windings each of substantiallylow resistance,- one of which is arranged in each of said branches, saidwindings being employed to step-up the resistance of said devices to anydesired value.

2. A substation circuit comprising two branches, a receiver having twowindings between which there is a high mutual inrpedance, one windingbeing arranged in each branch, a device consisting of a diaphragm andtwo buttons for converting sound waves into electric waves, and meanssimultaneous ly actuating the buttons of said device.

A substation circuit comprising upper and lower branches, a deviceconsisting of a diaphragm and two buttons on either side thereof, meansfor simultaneously actuating said diaphragm and said buttons, and areceiver having pair of closely coupled windings, one winding beingarranged in each of said branches.

i. A telephone circuit comprising upper and lower branches, a lineconnected to said upper branch, a two-element transmitter having oneelement in said upper branch and both elements in said lower branch, anda receiver having two closely coupled windings arranged on a singlecore, one winding being associated with each of said branches.

A. telephone circuit having two branches comprising a line, a receiverhaving two closely coupled windings, one winding being associated withthe first branch and the other winding being associated. with the secondbranch, a two-element transmitter arranged so'that one element is insaid first branch, and so that both elements are in said second branch,the windings of said receiver functioning to step-up the transmitterresistances and being proportioned so that said receiver may be madesubstantially anti-side tone.

6. In combination, a line, a two-element transmitter, and a receiverhaving two Windings, one winding of said receiver, the line, and oneelement of said transmitter being included in one branch, the otherwinding of said receiver and both elements of said transmitter beingincluded in another branch, the windings of said receiver having a highmutual impedance and being proportioned so that the side tone may belowered to a predetermined value.

7. In a telephone circuit, in combination, two devices for convertingsound waves into electric waves, and a receiver having two windings,said windings being so proportioned that when said devicessimultaneously actuated by a sound wave only current below apredetermined amount will flow in said receiver, the windings of said receiver having a high mutual imnedance.

8. In a telephone circuit, in combination two devices for convertingsound waves into electric waves, and a two-winding, electro magneticreceiver connected thereto, the wirulings of said receiver being closelycoupled and being so proportioned that the current flowing through saidreceiver will be limited to a predetermined value when sound wavesactuate said devices.

in testimony whereof, we have signed our names to this specificationthis 27th day of May, 1925.

FREDERIQK W. liloKO /VN. EGINHARD DIETZE.

